[TGS]

Here's a quote from Last Night at Twisted River by John Irving

Before the advent of mechanical loaders, the logs were unloaded by releasing trip bunks on the sides of the trucks—this allowed an entire load to roll off a truck at once. But the trip bunks sometimes failed to release; the men were occasionally caught under a cascade of logs while they were trying to free a bunk.

Now I, and I suspect most people unfamiliar with mid-twentieth century north American logging practices, have no idea what a "trip bunk" is. John Irving is not a stupid man and I am guessing he didn't assume that most of his readers would know what a "trip bunk" is. So, he included a noun that he knew that most people would not understand. Why do you think he did that?